The Numbers in Our Words: Words of Estimative Probability

Toward the end of this month I will almost certainly post the traditional Lone Gunman Year in Review post. Exactly how likely am I to do this? Am I able to quantify the probability that I’ll do this? By using the phrase “almost certainly”, I already have. To provide unambiguous, quantitative odds of an event occurring based solely on word choice, the “father of intelligence analysis”, Sherman Kent, developed and defined the Words of Estimative Probability (WEPs): words and phrases we use to suggest probability and the actual numerical probability range to accompany each. Kent’s idea has had a mixed reception in the intelligence community and the disregarding of the practice has been blamed, in part, for the intelligence failings that lead to 9/11. The words by decreasing probability:
  • Certain: 100%
  • Almost Certain: 93% ± 6%
  • Probable: 75% ± 12%
  • Chances About Even: 50% ± 10%
  • Probably Not: 30% ± 10%
  • Almost Certainly Not: 7% ± 5%
  • Impossible: 0%
(Graph from the CIA’s Psychology of Intelligence Analysis and 2012’s Critical Thinking for Strategic Intelligence.)
The practice has also gained some advocates in medicine, with the following list of definitions formed:
  • Likely: Expected to happen to more than 50% of subjects
  • Frequent: Will probably happen to 10-50% of subjects
  • Occasional: Will happen to 1-10% of subjects
  • Rare: Will happen to less than 1% of subjects
It would be nice if there were such definitions for the many other ambiguous words we use daily.